1. Field of the Invention
The present invention relates to a new device for controlling the performance of pumps having a constant volume, in particular for pneumatic pumps having a constant volume.
In their non-sucking version, working with compressed air or any other pressurized gas, such pumps are commonly used for pumping pulps and sludges of any kind (charged or uncharged liquids, acid or not) the temperatures of which do not exceed 100.degree. C. in general.
Under some acidity and abrasive conditions to which pneumatic pumps are commonly submitted, centrifugal pumps have the drawback that they require frequent replacing of the rotors, which is very expensive both for the replacement parts and for dissassembling and remounting.
For pneumatic pumps with membranes, the life-time thereof does scarcely exceed a few months even in the most favorable conditions.
This is the reason why pneumatic pumps without membranes find an important field of application, in particular in the draining of decantation vessels and open air tanks.
2. Description of the Prior Art
The main drawback of the pneumatic pumps with a constant volume was however, until now, the absence of any efficient regulation of their performance.
The performance of such pumps may indeed theoretically be controlled in two different ways: either by subjecting the admission and evacuation of pressurized gas to the level of liquid in the pump body, or by timing the relative duration of the admission and the evacuation of the pressurized gases.
The first method has however, until now, the drawback that there was no means both sufficiently inexpensive and reliable for detecting the level of charged liquids.
The second method has on the other hand never led to any satisfactory results in practice, because the important changes of drop of charge when pumping pulps and sludges, often gave rise to the carrying along of compressed air at the pump outlet during delivery of pumped liquid, and/or to overfilling of the pump body during "aspiration" (evacuation of compressed air), owing to an uneasy timing of the duration of admission and/or evacuation of the pressurized gas.
It is known to provide a device for controlling the performance of pumps comprising a pump body for the filling/delivery of a fluid, more in particular for pneumatic pumps without membranes, which device avoids the above stated drawbacks.
Said device therefor comprises liquid level detectors which cooperate with a float in order to control the filling and delivery operation of pumped liquid into and out of the pump body.